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By Robert LangrethBloomberg News • Saturday May 18, 2013 6:05 AM

NEW YORK — Two drugs from Bristol-Myers Squibb shrank tumors in as many as half of patients with
advanced melanoma, according to early research that might pave the way for drug combinations that
trigger the immune system to destroy cancer.

In the study, 52 melanoma patients were simultaneously treated with Bristol-Myers’ melanoma drug
Yervoy and nivolumab, its experimental therapy that focuses on the immune system. Tumors shrank in
40 percent of patients, and in 53 percent of those who got the most-effective dose combination,
according to data released on Wednesday before the American Society of Clinical Oncology meeting
that’s scheduled to begin on May 31.

“The responses are occurring faster and the absolute amount of shrinkage is more than we have
seen with either drug alone with this frequency,” said Jedd Wolchok, an oncologist at Memorial
Sloan-Kettering Cancer Center in New York and the study’s lead author. “What we are seeing that is
so impressive is the number of patients that have had very deep responses, their tumor burden
decreasing by 80 percent or more.” Tumors disappeared entirely in 10 percent of patients, he
said.

The new drug is designed to prevent flicking what is essentially a molecular off switch, called
PD-1, for immune system T-cells, the body’s key defenders against attacks by dangerous germs and
infections. Many tumors may hide from the immune system by triggering this switch.

While none of the drugs has been shown in large trials to extend life, doctors are awaiting
early results to gain clues about which drugs might work best in which patients.

Data was also released on Wednesday from a preliminary study of Merck’s lambrolizumab, which
also works on the PD-1 system. It shrank tumors in at least 35 percent of patients with advanced
melanoma, according to an abstract posted on the American Society of Clinical Oncology website.

In a third study, Roche’s experimental drug MPDL3280A reduced tumor size in 29 of 140 patients
with a variety of late-stage cancers. The drug helped those with lung cancer, melanoma, kidney
cancer, colorectal cancer and stomach cancer.